Ultra high frequency detector



Oct. 22,1946. A. E. ANDERSON 2,409,603

ULTRA HIGH FREQUENCY DETECTOR I Filed Sept. 24 1941 3 Sheets-Sheet l l l lzl l l I A TTORNE Y Oct. 22, 1946. A. ANDERSON ULTRA HIGH FREQUENCY DETECTOR Filed Sept. 24, 1941 3 Sheets-Sheet 2 FIG. 3

INVENTOR By A. EANDERSON WM Oct. 22, 1946. u I ANDERSON Y 2,409,608

- ULTRA HIGH FREQUENCY DETECTOR Filed Sept. 24, 1941 3 Sheets-Sheet 3 A TTORNEV ES ATNT QFFHCE ULTRA HIGH FREQUENCY DETECTOR Alva Eugene Anderson, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application September 24, 1941, Serial No. 412,065

1 Claim. (Cl. 25020) This invention relates to electron beam devices, particularly for operation at ultra-high frequenc1es.

An object of the invention is to intermodulate wave energies by virtue of non-linear actions in electron beams associated with a plurality of electrodes, particularly for use in frequency shifting arrangements for radio repeaters, first and second detectors in superheterodyne receiving sysclosures or chambers 4 and 5 are associated with certain electrodes within the envelope l. The resonating chamber 4 is designated as the input resonator and is provided with any suitable means 6 for the introduction thereinto of an incoming electromagnetic wave. A source I of electromotive force of relatively low frequency is associated with one of the elements of the electron gun 2. The resonator 5 is provided with means tems, and the like. 8 for leading away therefrom developed or am- Another object is to improve and stabilize the plified energy in theform of an electromagnetic operation of electron beam devices. wave. The electron gun 2 is provided with an A feature of the invention is a method of freelectron emitting cathode 9 which is associated quency conversion employing combinations of with any suitable heating means energized, for velocity variation and density variation effects in example, through leads I0 and II by a source l2 an electron stream with the aid of resonating of electromotive force. Associated with the oathchambers. ode 9 is an electrode l3 for use in regulating A further feature is a detector making use of and varying current of the electron beam and a varying electron current intercepted by an commonly known as an accelerating electrode. apertured electrode, the amount of current inter- It may be adjacent to and coaxial with the oathcepted being varied as the result of the shifting ode. A pair of suitably-shaped electrodes l4 and of a focal point of a focussed electron beam. [5 which may be fused into the walls of the enve- Another feature of the invention is an autolope I, define an input gap l5 and serve to close matic volume control employing variable electron the resonator 4 except for suitable apertures left velocities. in the electrodes for the passage of an electron Still another feature is the coupling of two beam or stream from the gun 2. The walls of resonators through a common wall thereof, both the envelope I serve to separate the resonators 4 resonators being also coupled to a common elecand 5 by a desired distance and to determine a tron beam. suitable drift space H. A pair of electrodes l8 Further objects and features of the invention and I9 define an output gap 20 associated with will be apparent from the following detailed dethe resonator 5. The resonators 4 and 5 may be scription and the accompanying drawings, while conductively connected together and to the colthe scope of the invention is defined in the aplector 3, making a system which is maintained pended claim. at a substantially constant potential difference In the drawings, from the cathode 9 by a source 2| of electro- Fig. 1 shows an arrangement for shifting from motive force, the negative terminal of which is one ultra-high frequency to another, as for examconnected to the cathode. A supplemental outple in a radio repeater; put means 22 is associated with the resonator 5,

Fig. 2 shows a superheterodyne receiving syspreferably in the form of a coaxial line, the inner tern employing features of the invention in conconductor of which is connected to an intermenection with the first detector stage; diate point 24 of the source 2! through a recti- Fig. 3 shows another form of superheterodyne fier 23. The rectifier is shunted by a parallel receiving system employing features of the invencombination of a resistor 25 and a condenser 26, tion in the first and second detector stages; the unit formed b the elements 23, 25 and 26 Fig. 4- shows an alternative form of first debeing serially inserted in circuit with the source tector; and l and the accelerating electrode IS. A stabilizing Fig. 5 shows a detector employing a focussed resistor 21 may be provided in the cathode lead. electron beam with variably displaceable focal The arrangement of Fig. l is adapted to effect point. a transfer of modulated energy from one high In the arrangement of Fig. 1 an envelope l frequency wave to another, both of which may of insulating a al is shown enclosing a plube in the ultra-high frequency range. In the rality of elements including an electron gun operation of the system an incoming wave of the shown generally at 2 and an electron interceptfrequency to which the resonator 4 is tuned, is ing or collecting electrode 3 referred tohereinintroduced through the input means 6 with the after as the collector. A pair of resonating enconsequent setting up of a high frequency alternating potential between the electrodes M and E in the input gap H6. The source I is arranged to operate at a frequency equal to the difierence which it is desired to introduce between the frequency of the incoming wave and the frequency of the outgoing wave. The resonator 5 is tuned to the frequency of the outgoing wave. The function of the source I is to superpose variations of the above-mentioned difference frequency upon the potential of the electron acceleratingvelocity in accordance with the variations of the incoming wave, is allowed to traverse the substantially field-free drift space H to permit further grouping of the electrons to take place. In the absence of the density variations impressed upon the electron beam by the source l but in the presence of velocity varying potentials across the gap N5, the velocity variations tend to produce approm'mately proportional electron density variations at the output gap 26.

The effect of the superposed density variation in the beam current is to produce a variation in the number of electrons per unit time which are subjected to the velocity variation at the input gap. As a result, the electron density variation at the output gap 26 tends to be pro- 'portional to the product of the two superposed variations, thereby introducing components corresponding tointermodulation products, such as combination frequencies according to well-known principles. Any desired modulation product may be accentuated by dimensioning or tuning the resonator 5 to resonate at the frequency of the selected modulation product. For example, the component of frequency equal to the incoming frequency minus the frequency of source I may be selected by making the critical dimensions of the resonator 5 somewhat greater than those of the resonator 6 in such proportion as to tune the resonator 5 to the desired output frequency. With proper tuning, an electromagnetic wave of the selected frequency will be sustained in the resonator 5 and delivered to the ouput means 3. By making the resonator 5 somewhat smaller than the resonator l, on the other hand, the frequency component equal to the incoming frequency plus the frequency of source I may be selected. Of particular interest in the use of the arrangement of Fig. 1 as a radio repeater, the diiference between th input and output frequencies is utilized to avoid undesirable reaction of the output upon the input which would otherwise cause self-oscillations or fsinging in the repeater.

Automatic stabilization of the intensity of the output wave is provided by taking a sample of the output wave from the resonator 5 through the coupling means 22 and applying the sample wave to the rectifier 23. The time constant of the resistor-condenser combination 25, 26 is preferably adjusted to a suitable value to smooth out rapid variations of the rectified current, leavdisc 32.

ing slow changes of current to produce a varying potential difference across the elements in series with the steady biasing potential impressed upon the accelerating electrode H3. The circuit is so arranged that the potential difference across the resistor 25 opposes the potential of the source 2i in determining the resultant potential of the electrode l3. In the well-known manner of automatic control systems of this type, changes in the amplitude of the output wave due to variations of th input wave are minimized. If it is desired, instead, to emphasize amplitude changes to secure a volume expansion effect, the polarity of the rectifier 23 may be made the reverse of that shown.

Stabilization of the system against power sup ply fluctuations associated with the source 21 is provided by means of the resistor 27 in the cathode return lead. Changes in the cathode return current affect the potential difference across theresistor 2T inherently in the proper sense to minimize such current changes by controlling the effective voltage between the cathode on the one hand and the system comprising the resonators 4 and 5, collector 3, and associated electrodes on the other hand.

Arrangements for maintaining an electron beam in any other suitable manner may be substituted for th electron gun 2. Any suitable resonators and electrodes may be substituted for the corresponding elements illustrated provided only that means are present for superposing an amplitude or current density variation and an electron velocity variation upon an electron beam which beam is thereafter subjected to suitable conditions or manipulation which results in a regrouping of the electrical charges in the beam in some manner adapted to produce intermodulation of the original variations. The automatic control features and stabilizing elements may, of course, be either omitted or included, as desired.

Fig. 2 illustrates certain features of the invention embodied in a superheterodyne radio receiver. The facilities for producing the electron beam, the envelope l, the collector 3, and the input and output resonators and associated arrangements are substantially the same as in the system of Fig. 1, except that the output resonator 5' is tuned to the same frequency as the input resonator 4. Intermediate between the input and output resonators are two auxiliary chambers 28 and 29 having a common wall 39. The interiors of the chambers are shown coupled by means of a coupling loop 3| passing through an aperture in the Wall 3! Alternatively, the loop 3| may be omitted and the aperture itself may be suitably dimensioned to provide the coupling. If desired, an iris or other suitable arrangement may be used to secure a variable coupling. Conductively connected with the wall 30 is an electrode 32 comprising adisc with an axial aperture surrounded by a short tube 33. The resonators 28 and 29 are provided with electrodes 34 and 35 respectively having apertures aligned with the aperture in the Drift spaces 36 and 31 respectively are provided between the resonators i and 28 and the resonators 29 and 5. Electromagnetic focussing coils 38 and 39, respectively, may conveniently manent magnets may be substituted for the electromagnets. The collector 3 is connected by way of a tuned circuit 42 to the cathode 9. An intermediate frequency amplifier 43, a detector 44 and a translating device 55, such as a telephone receiver, are coupled in tandem arrangement with respect to the tuned circuit 32 in the conventional manner of a superheterodyne receiving system. The control elements 23, and 26 may be coupled to the output device 22 in a manner similar to that shown in Fig. 1. In this case, however, the control is shown applied to the potential of the resonating system instead of the electron accelerating electrode.

The operation of the system of Fig. 2 in its broad aspect is similar to that of any superheterodyne receiver. An input wave is impressed upon the resonator t through the input coupling 6 to impress velocity variations upon the electron stream which has also been given an electron density variation through the action of the local source i. The operation of the system differs from that of Fig. 1 among other particulars, in that the essential interrnodulation of the local and incoming waves is effected in a somewhat different manner. Intermodulation according to the scheme described in connection with Fig. 1 may also occur in the drift space 36 of Fig. 2, but by tuning the resonator 28 to the frequency of the incoming wave the intermodulation at this point may be subordinated to amplification of the incoming wave, the latter process being brought about by electron density variations serving to set up forced oscillations in the resonator 28. A portion of the energy of these oscillations is transmitted to the resonator 29 by means of a coupling loop 3! to produce a second and relatively intense velocity variation of the electron beam in the gap between electrodes 33 and 35. By electron drift action in the drift space 3? a further amplified electron density variation is produced in the gap 28, causing forced oscillations in the resonator 5. The amplified oscillations in the resonator 5 will impress a new and still further amplified velocity variation upon the electron beam before the beam enters the space between the electrode Iii and collector 3.

To obtain the desired intermediate frequency component which may be at the frequency of the difference between the incoming wave and the source if, velocity sorting of the electrons is effected by subjecting the beam to a retarding or reflecting field. The field is conveniently produced by connecting the collector 3 to the cathode 9 as illustrated, thereby placing the collector 3 at a potential considerably negative with respect to the potential of the electrode l9. Due to the reflecting field, the slower electrons passing electrode it are unable to reach the collector 3 and are turned back, but the faster electrons are able to enter the collector 3 and induce a pulsating current in the return circuit. The intermediate frequency component of the pulsating current is resonated by the tuned circuit 42, thereby supplying an input to the intermediate frequency amplifier @3. Intermediate frequency amplification and final detection as well as translation of the signal are accomplished in the usual manner as in any superheterodyne receiving system.

It is contemplated that the frequency of source I will be relatively low compared to the frequency of the wave incoming at the coupling 6, in which case the difference frequency will lie within the transmission band of the resonators l, 23, 29 and 5. If desired the transmission band may be widened by detuning slightly one or more of the resonators or by increasing the degree of coupling between resonators 28 and 29.

The system of Fig. 2 may be employed simply as a high frequency amplifier if desired, in which case, the high frequency output may be taken from the resonator 5' by any suitable output means such as the coupling 8 illustrated in Fig. 1 and the collector may be connected to the positive terminal of the source of biasing potential. Elements 42, 43, M and and source 5 may then be omitted.

The automatic control arrangementof Fig, 2 is shown as operating to control the average electron velocity at the electrode i4 thereby controlling the electron transit time through the drift spaces 35 and 3! and consequently controlling the gain of the device as a high frequency amplifier. With the rectifier 28 polarized in the direction indicated by the arrow the control is such as to minimize volume changes. If instead, it is desired to emphasize the volume changes to give a volume expansion effect, the polarity of the rectifier should be reversed.

Fig. 3 shows a superheterodyne receiving system employing two electron beam devices in a tandem arrangement. In the first tube, shown at the top of the figure, the incoming wave is impressed upon the resonator G by means of the coupling 5 to produce a velocity variation in the electron beam at the gap :6. Conversion of the velocity variations into current density variations i provided for in the drift space ll. The local oscillations are generated in a resonant chamber of concentric structure having an outer wall 50, and inner walls 5!, 52, 53 and M, of which 52 and 53 are conductively connected with the outer wall I by wires 88 and 38, respectively. The wires are preferably of sufiiciently small dimensions not to interfere materially with the transmission or oscillation of electromagnetic waves within the enclosure. The wires preferably extend radially or substantially perpendicular to the electrical lines of force normally existing therein. Three gaps 55, '56 and 57 are provided along the course of the electron beam separated by additional drift spaces 58 and 59. The electrode I851 together with an electrode I8! defines the gap and the gaps '55 and 57 are defined by similar pairs of electrodes. The ends of the resonating chamber are closed by means of annular pistons 6t and SI, which are slidable for purposes of tuning the resonant chamber. The collector 3 is conductively connected to the inner conductor 6 of a concentric transmission line of which a tube '65 of conductive material connected conductiv'ely with the walls of the resonanting chamber is the outer conductor. The conductor 6 is connected to the tuning chamber and to ground through a high frequency choke coil 86. The concentric line 64, is connected to another concentric line 68 of smaller diameter through a tapering section 67.

a A second electron beam tube serving as an amplifier and second detector is shown in the lower portion of the figure and has an input resonator 82 coupled to the transmission line 68 by means of a coupling loop 69 inside the resonator. The wave impressed upon the resonator 62 produces a velocity variation of the electron beam at an input gap ll]. Velocity sorting is effected in the output gap ll due to the steady difference of potential maintained between insulated portions 82 and '83 of an output resonator by the electromctive force of a biasingsource 84. The slower electrons of the beam are turned back and only the faster electrons continue, finally striking a collector 12. A coupling transformer 13 is pro- 7 vided for repeating the alternating portion of the pulsating current in the collector lead and a translating device such as a telephone receiver 14 is connected to the secondary of the transformer I3.

In the operation of the system of Fig. 3 the incoming oscillation and local oscillations are combined in the first or upper tube to produce a wave of somewhat lower frequency corresponding to the usual intermediate frequency wave. The wave so produced is amplified by the second or lower tube and the signals are detected by the velocity sorting process above described. The local oscillator is substantially a, two-stage amplifier with coupling between the output and input. The relative voltages impressed upon the input gap 55 and the output gap 51 may be adjusted by proper setting of the tuning pistons 60 and BI, a movement of both pistons in thesame direction an equal amount having substantially no effect on the resonant frequency. I If it is desired to operate the lower tube at a much lower frequency, e. g. in the ordinary intermediate frequency range, the second tube may be replaced by a conventional intermediate frequency amplifier.

Fig. 4 shows another arrangement for the first detector of a superheterodyne receiving system. A resonant chamber 90 is tuned to the incoming frequency. Another resonant chamber SI having a wall in common with the resonator 90 is tuned to the frequency desired for the local or beating oscillator. A gap 92 is provided within the resonator 90 and gaps 93 and 04 within the resonator The collector 3 is connected to the biasing potential source through a tuned circuit which may be tuned to the difference frequency.

In the operation of the arrangement of Fig. 4 the electron beam receives a velocity variation in accordance with the incoming waves at the gap 92. The beam receives a second electron velocity variation at the gap 93 in accordance with the local oscillations. The electron path between the gap 93 and the collector 3 is essentially a drift space and due to the non-linear character of the drift space action, difference frequency components are set up in the electron density variations efiected by the drifting of the electrons. The gap 94 is provided for the purpose of extracting enough energy from the electron stream to support continuous oscillations in the resonator 0%. The intermediate frequency wave may be of sufficiently low frequency to be handled with ordinary tuned circuits, and any desired utilization device, such as an intermediate frequency. amplifier, may be coupled to the tuned circuit '95 in well-known manner.

Fig. 5 shows an alternative form of detector which may be used either as a first or second detector in a superheterodyne receiving system or as a simple detector for the direct conversion of an ultra-high frequency wave to recover the original signals in a single step of detection. A

resonator I00 is provided for the input wave and is associated with a gap IOI. Separated from the first gap by a space I02 are a pair of connected electrodes I03 and E04, which may be like the electrodes shown herein for the accommodation of a resonating chamber, but with the chamber omitted. The electrodes I03 and I04 are connected to the positive terminal of the biasing potential source through a resistor I05 which is shunted by a translating device such as a telephone receiver I06. A single electronpermeable electrode of any suitable type may be second-mentioned used instead of the connected electrodes I03 and I04. Focusslng means such as an eleotromagnet I01 energized in any suitable way as for example by a battery I08 is provided to bring the electron beam to a focus near the electrodes I03 and I04. 7

In the operation of the system of Fig. 5 the incoming wave is resonated in the chamber I00 and by means of the gap IOI impresses a velocity variation upon the electron beam. The electron gun 2 is preferably of a type which focusses or concentrates the electron beam, and arranged to establish a focal point in the gap I M. The focussing coil I01 normally produces a point of concentration of the beam in the neighborhood of the electrodes I03 and I04. The electron velocity variation impressed upon the beam is arranged'to be sufiicient to cause a shifting of the point of concentration axially with respect to the electrodes I03 and I04 in accordance with amplitude modulations of the incoming wave. The electrodes I03 and I04 are thus caused to intercept a variable portion of the electrons of the beam, thereby producing a pulsating current through the resistor I 0 5 and receiver I06. If desired, the resistor I 05 may be replaced by a tuned circuit resonant to a desired intermediate frequency and the voltage variations in this tuned circuit may be employed to excite an intermediate frequency amplifier.

What is claimed is:

A modulating system comprising an electron beam-type tube, a plurality of resonating chambers arranged in succession along the path of the electron beam, one of said resonating chambers having two electron permeable electrode portions in opposite walls, in alignment with the electron beam to permit the beam to traverse said resonating chamber, another of said resonating chambers being located beyond said firstmentioned resonating chamber and enclosing a drift tube and having two electron permeable electrode portions in opposite walls, said electrode portions and the axis of said drift tube being in alignment with the electron beam, said resonating chamber being resonant at a frequency difierent from the resonant frequency of the first-mentioned resonating chamber, a source of electroenagnetic waves coupled to said first-mentioned resonating chamber to excite forced oscillations therein and to impress an electron velocity variation upon the electron beam at the frequency of said forced oscillations as the beam traverses the resonating chamber, a substantially field-free drift space between said first and second-mentioned resonating chambers for converting the said velocity variation of the electron beam into a corresponding electron density variation, means including the said electron permeable electrode portions of said second-mentioned resonating chamber and the said drift tube enclosed within said resonating chamber for generating selfoscillations in said second mentioned resonating chamber and for impressing upon the said density varied electron beam at a point ahead of said enclosed drift tube, a second velocity variation at the frequency of said self-oscillations and means including the said enclosed drift tube for converting the compound variation of the electron beam so produced into a second electron density variation comprising an intermodulation of said forced oscillations and said self-oscillations.

ALVA EUGENE ANDERSON. 

